1. FIELD OF THE INVENTION
The present invention relates to a color photographic light-sensitive element, more particularly, it relates to a method for preventing the fading of a magenta dye image which is formed upon coupling of an anilino type coupler with an oxidation product of a paraphenylenediamine or a derivative thereof due to light and/or heat and preventing the discoloration in non-color image areas.
2. DESCRIPTION OF THE PRIOR ART
Color photographic light-sensitive elements are, in general, prepared by coating on an appropriate support a silver halide emulsion containing couplers dispersed therein. Conventional color photographic light-sensitive elements are produced by dispersing couplers capable of forming cyan, magenta and yellow dyes upon coupling with the oxidation products of color developing agents into a red-sensitive, green-sensitive and blue-sensitive silver halide emulsions, respectively, and coating these emulsions in an appropriate order on a support.
Color photographic light-sensitive elements thus produced are subjected, after exposure, to a series of processing steps such as color development, bleaching, fixing, stabilizing, etc., to form final color images. In such a processing, color dye images are formed together with silver images in a color developer solution containing a color developing agent and then the silver images are oxidized in a bleaching solution and subsequently removed with a fixing solution. The bleaching step and the fixing step can also be carried out in a mono bath of bleach-fixing solution. It is also known to add a subsequent step with a bath for stabilizing the dye images thus formed.
Recently, an intensification process in which similar color dye images are formed, but using several tenths of the amount of silver halide present in an ordinary light-sensitive element, has been developed. A cobalt (III) complex salt as described in Japanese patent application (OPI) No. 9728/1973 (corresponding to U.S. Pat. No. 3,834,907) and a peroxide as described in German patent application (OLS) No. 1,813,920 are known as intensifying agents. In such a processing, silver images and color dye images are formed in a color developer solution just as in a conventional process and dyes are further formed by the reaction of a coupler with a color developing agent oxidized with an intensifying agent in the presence of silver as a catalyst. Thus, a reduced amount of silver such as only several tenths of the amount present in an ordinary color photographic element is employed and such a process is suitable for conservation of natural resources. After the intensification step the silver is removed with bleaching and fixing steps and the dye images remain in the photographic element. The dyes formed in both processes are the same azomethine dyes or indoaniline dyes.
The photographic images thus obtained are often stored as record for a long period of time or are exhibited. However, the photographic images are not sufficiently stable to light, heat and/or humidity and when the photographic images are exposed to light for a long period of time or stored under conditions of high temperature and high humidity, a fading or discoloration of the dye images and a discoloration of non-image areas usually occur resulting in a deterioration of the image qualities.
5-Pyrazolone type compounds are widely used as a photographic magenta coupler. When a light-sensitive element having a photographic layer containing a silver halide emulsion and a coupler are exposed through an optical wedge and developed in a developer solution containing a developing agent such as paraphenylenediamine, a large amount of dye is formed upon coupling of the coupler with the developing agent and a small amount of coupler which does not form a dye remains in areas subjected to a large amount of exposure. On the other hand, in areas subjected to a small amount of exposure the coupler which does not form a dye remains in a large extent and in areas which were not exposed none of the coupler forms a dye and all of the coupler remains. The unexposed areas are non-image areas.
It is known that dyes formed from 3-acylamino-5-pyrazolone couplers of the class of 5-pyrazolone couplers are converted by means of heat into their leuco forms and thus fading occurs where residual coupler is present.
Accordingly, a subsequent development bath treatment with a solution containing formaldehyde is conventionally employed in order to deactivate remaining couplers. However, it is desirable to omit this treatment since formaldehyde is poisonous to the human body. On the contrary, fading of the image formed from 3-anilino-5-pyrazolone couplers does not occur due to heat even in the absence of treatment with a bath containing formaldehyde in processing steps and also these couplers have many superior properties such as color hue of the dyes formed therefrom.
Therefore, many investigations have been made on 3-anilino-5-pyrazolone couplers and examples of 3-anilino-5-pyrazolone couplers are described in U.S. Pat. Nos. 3,127,269, 3,615,506, 3,684,514 and 3,935,015.
However, 3-anilino-5-pyrazolone couplers are unstable to light in comparison with 3-acylamino-5-pyrazolone couplers and the particular disadvantage in that when unexposed areas in which a large amount of coupler remains are exposed to light for a long period of time a yellow stain occurs is encountered. It is known, however, that in order to prevent the formation of such a yellow stain due to light, a hydroquinone derivative such as di-tert-octylhydroquinone or a phenol derivative can be used in combination therewith. Examples are described, for example, in British Pat. No. 1,347,556 and Japanese patent application (OPI) No. 134,327/1974 (corresponding to U.S. Pat. No. 3,930,866).
Further, it is also known that 3-anilino-5-pyrazolone couplers having a group which prevents fading incorporated in the molecule thereof show reduced formation of yellow stain due to light as a result of the fading preventing group such as a phenoxy group in the molecule thereof as described, for example, in U.S. Pat. No. 3,519,429 and Japanese Patent Application (OPI) No. 110,344/1974.
The extent of yellow stain preventing effects by such a hydroquinone derivative or a phenol derivative depends largely on the structure of the oil solubilizing group of the 3-anilino-5-pyrazolone coupler. For example, a 3-anilino-5-pyrazolone coupler characterized by its oil solubilizing group and represented by the general formula (I) shown below: ##STR5## wherein R represents an alkyl group having 2 to 22 carbon atoms; and A represents a phenyl or naphthyl group substituted with one or two lower alkyl groups is advantageous because yellow stain formation is small and such is further reduced by the presence of an alkylhydroquinone compound therewith but this coupler type has the disadvantages that the solubility in a high boiling organic solvent such as dioctyl butyl phosphate is low, the coupling reactivity is low and the preparation thereof is difficult.
It is desired to develop a method for improving these characteristics and yet retain the small amount of yellow stain due to residual coupler remaining when using an alkylhydroquinone compound in combination therewith.
On the other hand, a 3-anilino-5-pyrazolone coupler characterized by the oil solubilizing group thereof and represented by the general formula (II) shown below has the advantages of good solubility, a high coupling reactivity and ease of preparation. However, the coupler is disadvantageous in that the stability of the color image formed is inferior and a large amount of yellow stain due to residual coupler occurs when it is exposed to light for a long period of time and in that this yellow stain due to light is prevented to a lesser extent by use of an alkylhydroquinone compound in combination therewith.